One of the desired attributes of material employed by dentists for taking impressions of teeth is that the material, applied in a semi-fluent form, will set up rapidly to form the desired impression. Many materials suitable for this purpose are known. In the usual case, the impression material is mixed from two constituents which are kept separate from each other and mixed only immediately prior to use. The mixed material is applied to the area of which an impression is desired normally by a syringe having a relatively large nozzle which, for pusposes of description is conveniently termed a dental impression gun.
Impression materials presently in use are agar hydrocolloids, polysulfide rubbers, silicone rubbers, and alginate hydrocolloids. The latter material is considerably more viscous than the others.
After the material is mixed, it must be loaded into the gun and the gun prepared for operation. The usual technique it to remove the plunger, or the nozzle, from the gun, see U.S. Pat. No. 3,436,828, and introduce the mixed material into the gun barrel from the plunger end. The plunger is then reinserted into the barrel. While this operation is not complex, it must be recalled that the material normally is quite viscous and thus cannot be introduced into the barrel rapidly. Consequently, a substantial amount of time is consumed in transferring an adequate amount of the impression material from the mixing vessel to the relatively small opening defined by the diameter of the gun barrel. Because the material begins to set as soon as it is mixed, its properties of flowability rapidly deteriorate, thus increasing the possibility that the material when dispensed from the gun may be too stiff to fill all of the minor recesses and crevices in the region to which it is applied, thus resulting in an unsatisfactory impression.
This problem has been recognized in the prior art; see for example Hickes U.S. Pat. No. 2,825,134 in which a rather complex arrangement is provided so that mixing of the two constituents of the impression material can take place in the barrel of the gun.
The present invention is especially directed to various forms of dental impression guns designed to facilitate the rapid loading of an adequate quantity of a fast setting impression material into the barrel of the gun.